Return Result<Self, Self::Err> in FromStr impls

If we return `Self, Self::Err` then the implementations of `FromStr` are
easier to maintain.

Author: tcharding

src/ecdh.rs

@@ -79,7 +79,7 @@ impl SharedSecret {
 
 impl str::FromStr for SharedSecret {
     type Err = Error;
-    fn from_str(s: &str) -> Result<SharedSecret, Error> {
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
         let mut res = [0u8; SHARED_SECRET_SIZE];
         match crate::from_hex(s, &mut res) {
             Ok(SHARED_SECRET_SIZE) => Ok(SharedSecret::from_bytes(res)),

src/ecdsa/mod.rs

@@ -37,7 +37,7 @@ impl fmt::Display for Signature {
 
 impl str::FromStr for Signature {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Signature, Error> {
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
         let mut res = [0u8; 72];
         match from_hex(s, &mut res) {
             Ok(x) => Signature::from_der(&res[0..x]),

src/key.rs

@@ -111,7 +111,7 @@ impl ffi::CPtr for SecretKey {
 
 impl str::FromStr for SecretKey {
     type Err = Error;
-    fn from_str(s: &str) -> Result<SecretKey, Error> {
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
         let mut res = [0u8; constants::SECRET_KEY_SIZE];
         match from_hex(s, &mut res) {
             Ok(constants::SECRET_KEY_SIZE) => SecretKey::from_slice(&res),
@@ -164,7 +164,7 @@ impl fmt::Display for PublicKey {
 
 impl str::FromStr for PublicKey {
     type Err = Error;
-    fn from_str(s: &str) -> Result<PublicKey, Error> {
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
         let mut res = [0u8; constants::UNCOMPRESSED_PUBLIC_KEY_SIZE];
         match from_hex(s, &mut res) {
             Ok(constants::PUBLIC_KEY_SIZE) =>
@@ -1128,7 +1128,7 @@ impl fmt::Display for XOnlyPublicKey {
 
 impl str::FromStr for XOnlyPublicKey {
     type Err = Error;
-    fn from_str(s: &str) -> Result<XOnlyPublicKey, Error> {
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
         let mut res = [0u8; constants::SCHNORR_PUBLIC_KEY_SIZE];
         match from_hex(s, &mut res) {
             Ok(constants::SCHNORR_PUBLIC_KEY_SIZE) =>

src/schnorr.rs

@@ -64,7 +64,7 @@ impl fmt::Display for Signature {
 
 impl str::FromStr for Signature {
     type Err = Error;
-    fn from_str(s: &str) -> Result<Signature, Error> {
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
         let mut res = [0u8; constants::SCHNORR_SIGNATURE_SIZE];
         match from_hex(s, &mut res) {
             Ok(constants::SCHNORR_SIGNATURE_SIZE) =>